Conventionally, known are metal-air batteries that each use a metal as an active material of a negative electrode and oxygen in the air as an active material of a positive electrode. International Publication No. WO 2010/052336 (Document 1), for example, discloses a rechargeable zinc-air battery. It is described that in this battery, an anode includes essentially-spherical copper particles coated by a layer of zinc, and it is thereby possible to successfully charge the battery.
Incidentally, in secondary batteries such as metal-air batteries or the like, there is a possibility of causing a short circuit between the positive electrode and the negative electrode by occurrence of dendrites in which the metal is locally deposited on the negative electrode during charge. In the technique of Document 1, it is uncertain whether or not the occurrence of dendrites is suppressed.